1. Field of the invention
This invention relates to a carrying vehicle which is movable in all directions, comprising: vehicle wheels, and driving wheels with drive mechanisms for driving the vehicle wheels, in which each of the driving wheels are controlled with a steering mechanism so that its moving direction is controlled with the vehicle body maintained unchanged in heading.
2. Related Art
A carrying vehicle movable in all directions (such as an automated guided vehicle on which an article handling robot is mounted), as shown in FIG. 10, has a vehicle body 1; and three driving/steering units 3 arranged on the lower surface of the floor (bottom plate) 2 of the vehicle body 1. Each of the driving/steering units 3, as shown in FIG. 11, comprises: a steering mechanism 4 secured to the floor 2; and a drive wheel mechanism 6 coupled to the lower end of the steering shaft 5 of the steering mechanism 4. A driving wheel (or driving tire) 9 is fitted on the outer rotor 8 of a drive motor 7 of outer rotor type. On the vehicle body 1 are installed a battery, a power source unit such as a power converter for controlling the supply of power from the battery to the steering motor of the steering mechanism 4 and to the above-described drive motor, and a driving/steering control device for receiving feedback signals from the steering motor and the drive motor to control, for instance, the power converter.
FIG. 12 shows one example of a passageway along which the automated guided vehicle A moves. In FIG. 12, reference characters STA, STB and STC designate article handling stations in the yard.
When it is required for the automated guided vehicle A to approach any one of the article handling stations and stop there, its movement is limited by other devices (not shown) to some extent; that is, the automated guided vehicle A is forced to approach the station from a drive route while moving sideward which is spaced a certain distance from the line of the stations.
It is assumed that the automated guided vehicle A moves to the stations STA, STB and STC in the stated order; that is, it moves to positions 1, 2, 3, 4 and 5 in the stated order. During this movement, it is necessary to turn the driving wheels about their steering shafts 360.degree. in one direction. If the driving wheel is turned 360.degree. in one direction, then the power cables and the signal cables connected between the power source unit and the control device on the vehicle body and the steering mechanism and the driving wheel mechanism may be broken due to twisted.
In order to overcome this difficulty, the conventional automated guided vehicle is provided with a stopper or other suitable control means to prevent the angle of relative rotation of the vehicle from becoming more than 360.degree..
That is, when, in the case of FIG. 12, the vehicle is stopped at the position 2 or 4, a rest swing operation (in other words, a rest steering operation) is carried out; that is, only the steering shaft is turned 180.degree..
However, the rest swing operation raises the following problems: First of all, the rest swing operation takes a relatively long time. Furthermore, in the rest swing operation, the grounding surface of the driving tire is rubbed against the surface of the yard, so that the driving tire is worn; that is, it is lowered in durability. In addition, when the automated guided vehicle is used in the clean room, the particle produced by the rubbing of the tire cannot be disregarded.